Lecture 6 Perspectives on Medical Evolution and Introduction to Aging

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11 Apr 2012
Lecture 6 BIO220 Perspectives on Evolutionary Medicine and an Introduction to
Evolution an Medicine
Aging: proximate and Ultimate causes
Costs of reproduction
The evolutionary theories of aging
oMutation accumulation
oAntagonistic Pleiotropy
Evolutionary Medicine
Definition: applications of evolutionary principles to the problems of health.
Approach: asks why (ultimate) rather than how (proximate) questions
Utility: Better understanding = better prevention, treatment
Questions in Evolutionary Medicine
Is this response adaptive, and for whom?
When do we expect resistance to evolve?
When do we expect the evolution of extreme virulence?
Are there multiple origins of a disease?
Will vaccines lead to evolution of pathogens?
Why do we age?
Five reasons why we are vulnerable to disease
1. Trade-offs: structures and systems must balance conflicting demands.
Longevity vs. Fecundity
2. Environmental Change: Environments change at a rate that exceeds our rate
of evolution
3. Pathogen Evolution: Pathogens evolve faster than we do.
4. Historical contingency
5. Defenses: systems built for defense against pathogens and degradation
come at some cost.
What is aging or senescence?
Definition: Progressive decline in somatic function reflected in reductions in fertility as
well as survivorship.
Proximate cause: Progressive degeneration of the soma.
Manifestations of aging
General degeneration of the soma
oImpaired function
oIncreased disease
Mortality rate increases with age
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Senescence: An evolutionary mystery
Observation: We have evolved to age and die
Expanation: Appears to be non-adaptive in the extreme.
Aging at Different Rates
Humans and Fulmars, Mayfly (1 day adulthood), Bristlecone Pine (5000 years adulthood)
Free Radicals and Vitamins
oMolecules containing at least one unpaired electron
oAttack and modify macromolecules
oOxidation of DNA, proteins, lipids
oWe have our own defenses (various amino acids that act as antioxidants)
oVitamins E and C act as antioxidants
oWe also have repair mechanisms: Why not “enough” repair?
Life Without Constraints (Trade-offs)
Darwinian Demon
oThe ideal organism would maximize all fitness components simultaneously
oBegin reproducing at birth
oReproduce at an infinite rate
oLive forever
Biological systems are constrained
Constraints often take the form of trade-offs
Good for one fitness component but not for the other
Longevity vs. Fecundity
Trade-offs affect the evolution of all traits
oDisplay size (morphological trait)
oForaging Rate (Behavioral trait)
oLongevity (Life History Trait)
Trade-offs may govern the evolution of DNA repair mechanisms
DNA repair +for longevity, -for fecundity
High reproductive rate, increased senescence, decreased lifespan
Costs of reproduction
oHigh reproductive rates accelerate senescence and thereby shortens life span.
Reproductive effort+ for reproductive rate, -for longevity
Reproductive costs in waterstriders
Prediction: Females induced to reproduce at a high rate will have reduced longevity.
Test: Female Waterstriders
Hypothesis: High reproductive rates accelerate senescence and thereby shortens lifespan.
Design: Manipulated reproductive rates of females by changing food ration.
Data: reproductive rate and longevity.
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